Stainless steel, 30 inches wide, ventilation built in: the HMV3053U is a discontinued 300 Series unit with 1.6 cubic feet and 1,550 watts. Models from this generation are mostly about a decade old now, and one part has almost certainly been ignored the whole time, the ventilation damper inside.
The damper is a small hinged door in the vent path: it swings open with the blower and shuts when the fan stops. Old grease can make it stick open, and cold outside air then flows back down into the kitchen. Owners tend to blame drafty windows. Freeing or replacing the damper is a simple job and stops the draft at once.
Grease buildup can also seize the flap entirely. A separate age-related problem is cavity paint that blisters after years of use. That is a safety issue, since damaged paint leaves bare metal that may arc. We look at the damper first, then the cavity, and advise you plainly.
Likely the damper in the vent path has jammed open, usually because of old grease. Freeing it or fitting a new one is a simple fix, and the breeze stops right away.
No. With the coating gone, bare metal is exposed and may arc. Stop using the microwave and have it inspected, because this is one problem you should not run through.
Only if you can reach it safely with the power off and the unit cool. Many dampers sit behind filters and wiring. If it will not move freely, leave it to a technician.
Book in about a minute, or call the desk. Same-day windows inside the Loop on most days, next-day across the rest of Houston.